Method of transferring magnetic toner particles in an image configuration and apparatus therefor

ABSTRACT

Magnetic toner particles, adhered to an electrostatically charged photoconductive layer of a recording element in an image configuration, are transferred to the surface of a sheet of paper by (a) disposing the paper adjacent to the toner particles, (b) exposing the photoconductive layer to light to reduce the electrostatic attraction between the toner particles and the recording element; and, (c) applying a magnetic field between the recording element and the paper to attract the toner particles to the paper. The apparatus includes a transfer station where a light pipe exposes the photoconductive layer with light and a heater fixes the toner particles to the paper.

United States Patent 1191 Giaimo, Jr.

]March 20, 1973 METHOD OF TRANSFERRING MAGNETIC TONER PARTICLES IN AN IMAGE CONFIGURATION AND APPARATUS THEREFOR [75] Inventor: Edward Charles Giaimo, Jr., Princeton, NJ.

[73] Assignee: RCA Corporation, New York, NY. 22 Filed: April 16, 1971 [21] App1.No.: 134,770

[52] 1.1.8. Cl. ..96/l.4, 346/74 ES, 346/74 MP, 355/16, 355/17 [51 Int. Cl. ..G03g 13/14 [58] Field of Search.....355/3, 12, l6, 17; 346/74 ES, 346/74 MP; 96/1.4

[56] References Cited UNITED STATES PATENTS 3,392,642 7/1968 Germer ..355/3 3,250,636 ..346/74 MP 5/1966 Wilferth 3,284,196 11/1966 Mazza .355/17 X 3,185,777 5/1965 Rheinfrank ..355/1 7 X 3,414,409 12/1968 Gallo ..96/1 .4

Primary Examiner-Samuel S. Matthews Assistant Examiner-Fred L. Braun Attorney-Glenn H. Bruestle [57] ABSTRACT Magnetic toner particles, adhered to an electrostatically charged photoconductive layer of a recording element in an image configuration, are transferred to 10 Claims, 6 Drawing Figures PATENTEU MR 2 01975 To TEMPERATURE l3()& 32; CONTROLLER INVENTOR. 244 CURRENT 256 EdwardCGz'a'mo,Jr.

CONTROL BJ E,

A TTORNE Y PATEFHEUHARZOIGH 3 1,55

sum 2 BF 3 I N VEN TOR.

I Edward 61 Giaz'm0,Jr.

ATTORNEY METHOD OF TRANSFERRING MAGNETIC TONER PARTICLES IN AN IMAGE CONFIGURATION AND APPARATUS THEREFOR BACKGROUND OF THE INVENTION This invention relates generally to the art of electrostatic printing, and, more particularly, to a method of transferring magnetic toner particles in an image configuration and apparatus therefor. The novel method and apparatus are particularly suitable for transferring unfixed toner particle images from a master recording element to an inexpensive transfer sheet so that the master recording element may be reused.

It is a common practice in many electrostatic printing systems to transfer an unfixed powder (toner) image, adhered by electrostatic attraction to the surface of a recording element, to a transfer sheet by placing the transfer sheet in contact with the powder image and attracting the powder to the transfer sheet with an electrostatic field. Powder transfer techniques of this type, however, use relatively high voltage external electric fields with stringent requirements imposed on the conductivity of both the photoconductive layers substrate and the sheet to which the powder is transferred. It has also been proposed to use magnetic toner particles for the powder image and to effect the transfer of the powder image to a transfer sheet with the aid of a magnetic field. While such a method is satisfactory for certain applications, it sometimes leaves something to be desired because the magnetic field does not completely overcome the electrostatic field, and some of the magnetic toner particles adhere tenaciously by electrostatic attraction to the recording element, thereby preventing a complete transfer.

The novel method and apparatus are more efficient than the aforementioned prior-art means for effecting a transfer of magnetic toner particles from a recording element to a transfer sheet because the novel means utilize a combination of electrostatic and magnetic forces wherein the electrostatic force causing the toner particles to adhere to the recording element is reduced when the transfer is effected so that substantially all of the toner particles are magnetically attracted to the transfer sheet.

SUMMARY OF THE INVENTION Briefly, the novel method of transferring magnetic toner particles on a recording element to a surface of a transfer member comprises (a) disposing a surface of the transfer member adjacent to the toner particles, (b) reducing the electrostatic attraction between the toner particles and the recording element, and (c) applying a magnetic field between the recording element and the transfer member to attract the toner particles magnetically to the surface of the transfer member.

The novel apparatus for transferring the magnetic particles from a recording element to the surface of a transfer sheet comprises guide means, defining a transfer station, to dispose the surface of the transfer sheet adjacent to the toner particles. Means to reduce the electrostatic attraction between the toner particles and the recording element, means to attract the toner particles magnetically to the transfer sheet, and means to fix the transferred toner particles on the surface of the transfer sheet are cooperatively associated with the guide means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary, enlarged, side-elevational and partly schematic view of apparatus to illustrate the theory of the novel method;

FIG. 2 is a side-elevational view, partly schematic and partly in cross-section, of an electrostatic printing system, showing an enlarged view of one embodiment of the novel apparatus for transferring magnetic toner particles from an electrostatically charged recording element to a transfer member;

FIG. 3 is a cross-sectional view taken along the line 3-3 in FIG. 2 and viewed in the direction indicated by the arrows;

FIG. 4 is a cross-sectional view taken along the line 4-4 in FIG. 2 and viewed in the direction indicated by the arrows;

FIG. 5 is an end-elevational view of the novel apparatus shown in FIG. 2 (without the recording element and transfer member) showing, in addition, an adjustable electromagnet and adjustable guide means for the recording element and the transfer member;

' and FIG. 6 is an electrical circuit diagram for energizing the novel apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT The theory by means of which magnetic toner particles, adhered by electrostatic attraction to a photoconductive layer in an image configuration, can be transferred to a transfer member, in accordance with the novel method and apparatus, will be explained with the aid of the simplified apparatus shown in FIG. 1. Referring now to FIG. 1, there is shown a recording element 10 disposed in a magnetic field provided between a magnetic north pole l2 and a magnetic south pole 14 of a magnet. The recording element 10 is disposed against a baffle plate 16 that is opaque to light. The recording element 10 is adapted to be moved in the direction of an arrow 18, by any suitable means. The opaque baffle plate 16 is formed with an elongated slit 20 therein for light to pass therethrough and onto the recording element 10. A transfer member, such as a sheet 22 of paper, is disposed adjacent to, and preferably slightly spaced from, the recording element 10. The sheet 22 is adapted to be moved synchronously with the recording element 10 in the direction of an arrow 24 by any suitable means.

The recording element 10 comprises a light-trans mitting substrate 26, such as translucent paper or plastic material with a conductive coating, and a photoconductive layer 28, such as photoconductive zinc oxide dispersed in a suitable resin binder. The recording element 10 has an image-receiving surface 30 and is of the type described in both Chapter 9 of the book Photoelectronic Materials and Devices," edited by S. Larach and published by D. Van Nostrand Co., Inc., 1965, and in Electrofax Direct Electrophotographic Printing on Paper, by C. J. Young and H. G. Greig, RCA Review, December 1954, Volume XV, No. 4. Recording elements with photoconductive layers other than zinc oxide, as, for example, comprising polyvinyl carbazole, leucobase of malachite green, or titanium dioxide, may also be used.

Let it be assumed that the recording element 10 has been previously electrostatically charged in darkness, exposed to light images, and developed with magnetic toner particles 32 to provide an unfixed powder image in an electrostatic printing process of the type described in the aforementioned Young and Greig publication. If the image-receiving surface 30 of the photoconductive layer 28 had been charged negatively for example, and if the toner particles 32 are electrostatically neutral, that is, not electroscopic, each of the toner particles 32 has induced in it an electrostatic dipole, of the polarity indicated in FIG. 1. Thus, the toner particles 32 are adhered to the surface 30 of the photoconductive layer 28 by electrostatic attraction. Although magnetic toner particles 32 which are electrostatically neutral are preferred, the novel method, however, is not limited to their use, and electroscopic (charge carrying) magnetic particles may also be used.

The toner particles 32 comprise a core 33 of magnetic material coated with a coating 35 of a thermoplastic adhesive, as shown by the particle 32 in cross section. By the term: magnetic toner particles, as used herein, is meant toner particles of materials that are capable of being moved by a magnetic field. The cores 33 of the toner particles 32 may comprise nickel, cobalt, or soft iron particles, for example, capable of being attracted by a magnet. The average diameter of the toner particles is not critical. For example, magnetic toner particles of (a) nickel having diameters of between 5 and microns, (b) cobalt having an average diameter of microns, and (c) iron having an I average diameter of 20 microns provide very satisfactory images. The thermoplastic coating 35 of each toner particles 32 should be non-tacky, readily removable from an image-receiving surface, and fusible by heat or a solvent, whereby the transferred toner particles 32 can be permanently fixed to a transferred surface. The thermoplastic coating 35 may also comprise a magnetic material but this is not necessary if the core 33 is of a magnetic material. The toner particles 32 do not necessarily need to be spherical in shape. Suitable magnetic toner particles 32 for the novel method are described in U.S. Pat. Nos. 3,526,191; 3,106,479; and 3,093,039, for example. The toner particles 32 need not have an electroscopic charge to carry out the novel method because electrostatically neutral magnetic toner particles 32 are attracted to a charged surface by what is believed to be electrostatic induction.

The magnetic toner particles 32 are transferred from the surface 30 of the photoconductive layer 28 to the adjacent image-receiving surface 34 of the transfer sheet 22 at a transfer station 36. The dimensions of the transfer station 36 are defined, in part, by the area of the slit 20 in the opaque baffle plate 16.

Means are provided to decrease the electrostatic attraction between the magnetic toner particles 32 and the surface 30 of the photoconductive layer 28 at the transfer station 36 to effect a transfer of the toner particles 32. To this end, electromagnetic radiation, such as light, designated in FIG. 1 as hv, is directed through the slit 10 onto the translucent substrate 26 to render the otherwise darkened photoconductive layer 28 conductive at the transfer station 36. Thus, the light discharges the electrostatic charges on the recording element 10, at the transfer station 36, so that the magnetic toner particles 32 are free to be magnetically attracted onto the im age-receiving surface 34 of the sheet 22.

The transfer station 36 should be disposed to one side of a plane 40 of unstable magnetic equilibrium. The plane 40 of unstable magnetic equilibrium is defined herein as the plane wherein a magnetic body decreases its potential energy by any slight displacement from the plane. In other words, the instability of magnetic particles in the plane 40 is indicated by the face that they are attracted either toward the north or the south magnetic pole when slightly displaced either toward the north or magnetic south pole, respectively. In a uniform magnetic field, the plane 40 is equidistant from the north and south poles.

Before transfer from the surface 30 of the photoconductive layer 28 to the image-receiving surface 34 of the transfer sheet 22, each magnetic toner particle 32 may be considered to be acted upon by an electrostatic force Fe that is equal to, or greater than, an opposite force Fm, the force provided by the magnetic field. Since Fe is greater than Fm before light is allowed to fall on the photoconductive layer 28, it is possible for the magnetic toner image to enter the region wherein the magnetic field exists without being disrupted or destroyed.

At the transfer station 36, the electrostatic force Fe is diminished by the light hv impinging upon the photoconductive layer 28 (through the translucent substrate 26) and increasing its photoconductivity. Hence, the particles 32 at the transfer station 36 are now acted upon principally by the magnetic force Fm and move to the image-receiving surface 34 of the transfer sheet 22. Since the transfer station 36 is disposed on one side (south pole side) of the plane 40 of unstable magnetic equilibrium, each of the magnetic particles 32 moves (horizontally, as shown in FIG. I) from its position indicated by the particle 32a (in dashed line) to the position indicated by the particle 32b (illustrating its thermoplastic coating after being heated).

Means are provided to fix the magnetic toner particles 32 to the transfer sheet 22. To this end, heat is provided to the transfer sheet 22 to fuse the thermoplastic coating 35 of the toner particles 32 and thereby permanently adhere them to the image'receiving surface 34 of the transfer sheet 22, as illustrated by the particles 32b. When thus fixed, the transferred toner particles 32 may be moved out of the magnetic field and still retain their image configuration on the transfer sheet 22.

Referring now to FIGS. 2, 3, and 4, there is shown an electrostatic printing system 50 employing novel apparatus 52 for transferring magnetic toner particles 32 in an image configuration to a transfer member. In accordance with the method of electrostatic printing described in the aforementioned Young and Greig publication, an electrostatic image is developed on an image-receiving surface 54 of a photoconductive layer 56 of a recording element 58. The photoconductive layer 56, such as photoconductive zinc oxide in a resin binder, is adhered to a light-transmitting, or transluscent, substrate 60, such as a sheet of paper. The recording element 58 is in the form of a continuous web derived from a supply roll 62. The recording ele ment 58 is moved in the direction of arrow 64 by a motor 65 coupled to a take-up roll 67.

The recording element 58 is electrostatically charged in darkness at a charging station 66 by double corona discharge devices 68 and 70, as described in U.S. Pat. No. 2,922,883, so that the image-receiving surface 54 receives a uniform negative electrostatic charge. The surface 54 is exposed to a light image to be copied at an exposure station 72 to provide an electrostatic latent image of the image subsequently to be transferred. The surface 54 is exposed with light images from a photographic film 74 that is moved through a light projector 76 by a motor 78. The movement of the film 74 is synchronized with the movement of the recording element 58.

The electrostatic latent images on the image-receiving surface 54 are developed with magnetic toner particles 32 from a container 37. The magnetic toner particles 32 are brushed onto the electrostatic latent images on the surface 54 by a rotating brush 80, rotated by any suitable means (not shown).

The unfixed toner particles 32 on the surface 54 are transferred to an image-receiving surface 82 of a transfer member, such as a transfer sheet 84 of paper. The transfer sheet 84 is provided from a supply roll 86 in the form ofa continuous web. The transferring of the developed images occurs at a transfer station 88 defined by guide means of the apparatus 52. The guide means guide the developed recording element 58 and the transfer sheet 82 adjacent to each other at the transfer station 88 so as to effect the transfer of the magnetic toner particles 32 in an image configuration. To this end, a magnetic field is provided between a north pole 90 and a south pole 92 of a magnet which preferably is an electromagnet. Although a permanent magnet may be used, an electromagnet is preferable because it can provide a magnetic field wherein the magnetic force Fm can be controlled for the optimum transfer of magnetic particles for various values of electrostatic forces Fe that are encountered. Also, the magnetic field of an electromagnet may be eliminated easi ly when it is not desired to transfer magnetic particles.

An arcuate light pipe 94, one of the guide means, has an outer wall 96, comprising a portion of a cylinder, disposed between the magnetic poles 90 and 92. The light pipe 94 comprises a light-transmitting material, such as the plastic material Lucite." The outer wall 96 is coated with an opaque substance 98, such as an opaque black paint, except for three notched, lightemitting portions, 100, 102, and 104 immediately at the transfer station 88. An inner curved wall 106 of the light pipe 94 is formed with opposite parallel cavities 108 and 110 for receiving a pair of elongated lamps 112 and 114, respectively, therein. Except for the cavities 108 and 110, the inner wall 106 is also coated with the opaque substance 98. When the lamps 112 and 114 are connected in a suitable electrical cuicuit and lighted, light is transmitted through the material of the light pipe 94, emerging at the notched, uncoated portions 100, 102, and 104 of the light pipe 94 for the purpose hereinafter appearing. The light pipe 94 also provides guide means for guiding the recording element 58 into the magnetic field and through the transfer station 88. When the lamps 112 and 114 are energized from a variable voltage source, as will hereinafter be explained, the intensity of the light produced can be con trolled to adjust the electrostatic force Fe for providing an optimum transfer of magnetic particles 32 at a transfer station 88.

The novel apparatus 52 also includes means to guide the transfer sheet 84 through the transfer station 88 in a heated condition so as to fuse (fix) the thermoplastic coating 35 of the magnetic toner particles 32 to the image-receiving surface 82 of the transfer sheet 84. To this end, the transfer sheet 84 is pulled over an arcuate guide member 116, having an outer wall 118 and an inner wall 120, each a portion of a cylinder. The guide member 116 is made of a non-magnetic material, such as brass, and is disposed about the magnetic pole 92. A pair of massive, non-magnetic heat sinks 122 and 124 are fixed to opposite sides of the inner wall 120 of the guide member 116 by any suitable means (not shown). The heat sinks 122 and 124 are formed with through openings 126 and 128 for receiving heating cartridges 130 and 132 (represented schematically), respectively, therein. When the heating cartridges 130 and 132 are connected and energized in a suitable electrical circuit, they provide heat to the guide member 116. The transfer sheet 84 is pulled across the heated outer wall 118 of the guide member by the motor 65 that is coupled to a take-up roll 134 for the transfer sheet 84.

The light pipe 94 and the guide member 116 are guide means for guiding the recording element 58 and the transfer sheet 84, respectively, to the transfer station 88 where the magnetic toner particles 32 of developed images on the surface 54 of the recording element 58 are transferred to the image-receiving surface 82 of the transfer sheet 84. At the transfer station 88, the distance between the recording element 58 and the transfer sheet is preferably between about 1 and 3 mils, although this distance may vary from zero to more than 3 mils depending upon operating conditions, such as temperature, speed of travel of recording element 58 and transfer sheet 84, and melting point of the thermoplastic coating 35. The transfer station 88 is disposed on one side, the south magnetic pole 92 side, as shown in FIG. 2, ofa plane 136 of unstable magnetic equilibrium of the magnetic field provided by the magnetic poles 90 and 92. Thus, when the magnetic particles 32 reach the transfer station 88, light from the lamps 112 and 114, emerging through the lightemitting portions 100, 102 and 104 of the light pipe 94, exposes the previously charged photoconductive layer 56. Under these conditions, the photoconductive layer 56 becomes highly conductive so that the magnetic toner particles 32 are no longer adhered by electrostatic attraction to the surface 54 of the recording element 58, and the principal force now acting upon the toner particles 32 is the magnetic force produced by the magnetic field. Since the toner particles 32 at the transfer station 88 can now move in the magnetic field toward the south pole, they are magnetically attracted, in image configuration, onto the image-receiving surface 82 of the transfer sheet 84.

If the toner particles 32 were moved out of the magnetic field without first being fixed to the transfer sheet 84, they would lose their image configuration. Since the transfer sheet 84 is moved over the heated guide member 116 for a distance both before and after it reaches the transfer station 88, the thermoplastic adhesive coatings 35 on the toner particles 32 fuse and become fixed very quickly to the heated image-receiving surface 82 of the transfer sheet 84. Because of the gap between the light pipe 94 and the guide member 116 at the transfer station 88, the heat provided by the heating cartridges 130 and 132 fixes the toner particles 32 only to the image-receiving surface 82 of the transfer sheet 84, the gap functioning as a heat insulator for the recording element 58. Also, substantially no heat is transferred from the guide member 116 to the recording element 58 adjacent the light pipe 94 because the arcuate guide member 1 16 curves in an opposite direction from the arcuate light pipe 94. With this arrangement, any toner particles 32 remaining on the surface 54 of the recording element 58, after it has passed the transfer station 88, can be removed easily by any suitable means known in the art, such as a brush 140.

Referring now to FIG. 5, there are shown the magnetic poles 90 and 92 adjustably attached to a frame 150 of magnetic material, such as cold rolled steel, to provide an electromagnet structure. The magnetic poles 90 and 92 are provided with integral threaded studs 152 and 154 of magnetic material for adjustably mounting them through holes 156 and 158 in opposite parallel plates 160 and 162, respectively. The studs 152 and 154 are fixed to the plates 160 and 162 by nuts 164, and 166, respectively. The parallel plates 160 and 162 are spaced from each other by parallel rods 168 and 170. The rods 168 and 170 and the plates 160 and 162 provide a magnetic path for the magnetic flux generated by a pair of coils 172 and 174, disposed around the rods 168 and 170, respectively. The coil 172 has a pair of terminals 176 and 178, and the coil 174 has a pair of terminals 180 and 182. When the coils 172 and 174 are energized from a source of direct current, in a manner to be hereinafter explained, a controllable magnetic field is provided between the adjustable poles 90 and 92.

Means are provided to adjust the position of the light pipe 94 with respect to the guide member 116. To this end, a light pipe is provided with threaded studs 184 that are disposed through holes in the plate 160 and adjustably mounted on the plate 160 by nuts 186; and the guide member 116 is provided with threaded studs 188 disposed through holes in the plate 162 and adjustably mounted on the plate 162 by nuts 190. With this arrangement, the gap-192 between the light pipe 94 and guide member 116 can be adjusted to accommodate recording elements and transfer sheets of different thicknesses and to provide for an optimum transfer of toner particles 32. Thus, the gap 192 can be adjusted, if desired, so that the recording element 58 is in direct contact with the transfer sheet 84, rather than spaced therefrom. Such an arrangement may be desirable when the speed at which both the recording element 58 and the transfer sheet 82 is great enough through the transfer station 88 so that insufficient heat is transferred from the transfer sheet to the recording element 58 to fuse of the magnetic toner particles 32 to the recording element 58. Such an arrangement may also be desirable where the recording element 58 is disposable.

Referring now to FIG. 6, there is shown a circuit 200 for adjustably energizing the lamps 112 and 114 and the coils 172 and 174 of the electromagnet. To this end, a pair of wires 202 and 204 are connected to a suitable source 206 of ac voltage. A normally-open, triple-pole, single-throw relay switch 208 has two terminals 210 and 212 connected to the wires 202 and 204, respectively. A third terminal 214 of the switch 108 is connected through a relay coil 216 to one terminal 218 of a normally closed, stop switch 220. Another terminal 222 of the stop switch 220 is connected to the wire 204. The terminal 214 of the switch 208 is connected to a terminal 224 of a normally open, start switch 226. Another terminal 228 of the start switch 226 is connected to the wire 202.

When the start switch 226 is closed and the stop switch 220 is closed, the relay actuated switch 208 is closed to energize a variable transformer 230. Output terminals 232 and 234 of the transformer 230 are connected to the input terminals 236 and 238 of the lamps 112 and 114 to light them. When the switch 208 is closed, energy is also provided to an ac rectifier and variable dc current control 240, whose output terminals 242 and 244, in turn, are connected to the terminals 176 and 178 of the coil 172 and to the terminals 180 and 182 of the coil 174. The dc current sent through coils 172 and 174 are in such a direction as to make the pole a north pole and the pole 92 a south pole. Although the electromagnet, comprising the poles 90 and 92, is described herein as being energized by direct current, it is within the contemplation of the present invention to energize the electromagnet with alternating current also.

The voltage source 106 is connected to the heaters and 132 through a pair of output terminals 246 and 248 of a temperature controller 250. The temperature controller 250 is provided with a thermocouple sensor 252 for sensing the temperature of the guide member 116 so that the guide member 116 may be maintained at a desired temperature. The temperature controller 250 is of a type commercially available, such as temperature controllers made by Assembly Products, Chesterland, Ohio.

A normally-open, double-pole, single-throw relay switch 254 is connected in the circuit 200 to bypass the normally-open relay switch 208 when a relay coil 256 of the relay switch 254 is energized. With this arrangement, the lamps 112 and 114 and the coils 172 and 174 can be energized or de-energized at will by either energizing or de-energizing the relay coil 256 of the switch 254. Thus, the relay coil 256 may be energized at will from a separate voltage source (not shown) or automatically from a computer output (not shown) to selectively control the magnetic transfer of particles 32 from the recording element 58 to the transfer sheet 84. Also, with this arrangement, the transformer 230 can be adjusted to provide an optimum illumination of the lamps 112 and 114 for the most effective transfer of the magnetic particles 32 at the transfer station 88. The ac rectifier and variable dc current control 240, the dc current control of which may be a variable resistor, for example, provides means for adjusting the current through the coils 172 and 174, thereby controlling the strength of the magnetic field for an optimum transfer of toner particles 32 at the transfer station 88.

If it is desired to transfer developed images on the recording element 58 selectively to the im age-receiving surface 82 of the transfer sheet 84, either the relay switch 208 or the relay switch 254 can be opened when a transfer of the toner particles 32 is not desired. Hence, by selectively operating either of the relay switches 208 or 254, it is possible to edit the material transferred to the image-receiving surface 82 of the transfer sheet 84.

The novel method and apparatus, described herein merely for illustrative purposes, may be modified within the spirit of the invention. For example, means other than a light pipe 94 may direct light to the transfer station 88 for exposing the photoconductive layer 56 thereat. Also, the transfer sheet 84 may be heated before and after reaching the transfer station 88 by means other than the heating cartridges 130 and 132. it is also within the contemplation of the novel method and apparatus to provide a transfer sheet with a tacky adhesive material on its image-receiving surface for fixing uncoated magnetic toner particles thereon after they had been transferred thereto.

The novel method and apparatus provide transfer means of greater efficiency and applicability than that provided by the prior art because the novel means can substantially reduce the electrostatic forces, either contiriuously or selectively, that attract the toner particles to the recording element to provide a substantially complete transfer of the toner particles to the transfer sheet. Thus, particle transfers in very good image configuration are provided by the novel means. Also, the recording element can be substantially free of all toner particles after their transfer so that the recording element may be reused with little cleaning.

I claim:

1. In a method of the type wherein the photoconductive layer of a recording element comprising a photoconductive layer on a substrate, is electrostatically charged, exposed with a light image to provide an electrostatic latent'image, and developed with toner particles of magnetic material electrostatically attracted to said latent image to provide a powder image, the improvement of transferring the developed powder image to a surface of a transfer sheet comprising the steps of:

disposing said developed powder image at a transfer station, disposing said transfer sheet with its surface adjacent to, and slightly spaced from, said powder image at said transfer station, providing a magnetic field at said transfer station,

' reducing the electrostatic attraction between said toner particles and said photoconductive layer at said transfer station to cause said toner particles to be magnetically attracted to said surface of said transfer sheet, and

fixing said toner particles to said surface.

2. The method defined in claim 1, wherein said toner particles are coated with a thermoplastic coating, and

the step of fixing said toner particles comprises heating said surface to fuse said coating thereto.

3. The method defined in claim 1, wherein said substrate is light transmitting and the step of reducing the electrostatic attraction between said toner particles and said photoconductive layer at said transfer station comprises directing light to said photoconductive layer through said substrate.

4. The method of claim 1, wherein said toner particles are coated with a thermoplastic coating,

the step of disposing said developed powder image and said transfer sheet with its surface adjacent to, and slightly spaced from, said powder image comprises moving said recording element and said transfer sheet synchronously between two oppositely curved guide means, respectively, and

the step of fixing said toner particles to said surface comprises heating one of said two guide means to heat said transfer sheet, whereby to fuse said coating of said toner particles.

5. ln apparatus of the type wherein the photoconductive layer of a recording element comprising a photoconductive layer on a substrate, is electrostatically charged, exposed with a light image to provide an electrostatic latent image, and developed with magnetic toner particles adhered by electrostatic attraction to said latent image to provide a powder image, the improvement of means to transfer said powder image to a surface ofa transfer member comprising:

a transfer station,

means to dispose said recording element with said powder image at said transfer station,

means to dispose said transfer member with said surface adjacent to, but slightly spaced from, said powder image at said transfer station,

means to provide a magnetic field at said transfer station,

means to reduce the electrostatic attraction between said toner particles and said photoconductive layer at said transfer station and to cause said toner particles to be magnetically attracted to said surface of said transfer member, and

means to fix said transferred toner particles to said surface.

6. The apparatus of claim 5, wherein:

said means to dispose said transfer sheet with said surface adjacent to, but slightly spaced from, said powder image at said transfer station comprises an arcuate guide member, and

said fixing means comprises heating means cooperatively associated with said guide member for heating said transfer sheet at said transfer station. 7. Apparatus for transferring magnetic toner particles, adhered by electrostatic attraction in an image configuration on a recording element, to an imagereceiving surface of a transfer member, said apparatus comprising:

guide means to dispose said recording element adjacent said image-receiving surface of said transfer member with said toner particles facing said image-receiving surface at a transfer station,

means to reduce the electrostatic attraction between said toner particles and said recording element,

means to provide a magnetic field between said recording element and said transfer member to magnetically attract and thereby transfer said toner particles to said image-receiving surface,

said guide means comprising a light pipe for guiding said recording element to said transfer station, said recording element comprising a light-transmitting substrate and a photoconductive layer thereon, and said substrate facing said light pipe at said transfer station, and

said means to reduce the electrostatic attraction between said toner particles and said recording element comprising light-emitting portions in said light pipe at said transfer station to direct light to said photoconductive layer through said lighttransmitting substrate. 8. Apparatus for transferring magnetic toner particles, adhered by electrostatic attraction in an image configuration on a recording element, to an imagereceiving surface of a transfer member, said apparatus comprising:

guide means to dispose said recording element adjacent said image-receiving surface of said transfer member with said toner particles facing said im age-receiving surface at a transfer station,

means to reduce the electrostatic attraction between said toner particles and said recording element,

means to provide a magnetic field between said recording element and said transfer member to magnetically attract and thereby transfer said toner particles to said im age-receiving surface,

said magnetic toner particles comprising an electrically conductive core having a coating of a thermoplastic adhesive thereon,

said recording element comprising a light-transmitting substrate and a photoconductive layer thereon,

said guide means comprising a light pipe having a wall for guiding said recording member with its substrate facing said wall, said guide means also comprising a guide member having a wall for guiding said transfer member,

heating means being cooperatively associated with said guide member to heat it and said transfer member, and

said means to reduce the electrostatic attraction between said toner particles and said recording element comprising a light-emitting portion in said light pipe at said transfer station to direct light to said photoconductive layer through said lighttransmitting substrate.

9. Apparatus as defined in claim 8, wherein said wall of said light pipe and said wall of said guide member are arcuate in shape and curved in opposite directions, said walls being nearest to each other at said transfer station, and

said light pipe and said guide member are adjustably disposed with respect to each other.

10. In apparatus of the type wherein the photoconductive layer of a recording element comprising a photoconductive layer on a substrate, is electrostatically charged, exposed with a light image to provide an electrostatic latent image, and developed with magnetic toner particles adhered by electrostatic attraction to said latent image to provide a powder image, the improvement of means to transfer said powder image to a surface of a transfer member comprising:

a transfer station,

means to dispose said recording element with said powder image at said transfer station,

means to dispose said transfer member with said surface adjacent to, but slightly spaced from, said powder image at said transfer station,

means to provide a magnetic field at said transfer statron, means to reduce the electrostatic attraction between said toner particles and said photoconductive layer at said transfer station and to cause said toner particles to be magnetically attracted to said surface of said transfer member,

means to fix said transferred toner particles to said surface,

said means to dispose said recording element with said powder image at said transfer station comprising a light pipe with a wall for guiding said recording element to said transfer station, and

said means to reduce the electrostatic attraction between said toner particles and said photoconductive layer comprising light-emitting portions in said wall of said light pipe at said transfer station and a light source for providing light to said lightemitting portions at said transfer station, said substrate being light transmitting. 

3. The method defined in claim 1, wherein said substrate is light transmitting and the step of reducing the electrostatic attraction between said toner particles and said photoconductive layer at said transfer station comprises directing light to said photoconductive layer through said substrate.
 4. The method of claim 1, wherein said toner particles are coated with a thermoplastic coating, the step of disposing said developed powder image and said transfer sheet with its surface adjacent to, and slightly spaced from, said powder image comprises moving said recording element and said transfer sheet synchronously between two oppositely curved guide means, respectively, and the step of fixing said toner particles to said surface comprises heating one of said two guide means to heat said transfer sheet, whereby to fuse said coating of said toner particles.
 5. In apparatus of the typE wherein the photoconductive layer of a recording element comprising a photoconductive layer on a substrate, is electrostatically charged, exposed with a light image to provide an electrostatic latent image, and developed with magnetic toner particles adhered by electrostatic attraction to said latent image to provide a powder image, the improvement of means to transfer said powder image to a surface of a transfer member comprising: a transfer station, means to dispose said recording element with said powder image at said transfer station, means to dispose said transfer member with said surface adjacent to, but slightly spaced from, said powder image at said transfer station, means to provide a magnetic field at said transfer station, means to reduce the electrostatic attraction between said toner particles and said photoconductive layer at said transfer station and to cause said toner particles to be magnetically attracted to said surface of said transfer member, and means to fix said transferred toner particles to said surface.
 6. The apparatus of claim 5, wherein: said means to dispose said transfer sheet with said surface adjacent to, but slightly spaced from, said powder image at said transfer station comprises an arcuate guide member, and said fixing means comprises heating means cooperatively associated with said guide member for heating said transfer sheet at said transfer station.
 7. Apparatus for transferring magnetic toner particles, adhered by electrostatic attraction in an image configuration on a recording element, to an image-receiving surface of a transfer member, said apparatus comprising: guide means to dispose said recording element adjacent said image-receiving surface of said transfer member with said toner particles facing said image-receiving surface at a transfer station, means to reduce the electrostatic attraction between said toner particles and said recording element, means to provide a magnetic field between said recording element and said transfer member to magnetically attract and thereby transfer said toner particles to said image-receiving surface, said guide means comprising a light pipe for guiding said recording element to said transfer station, said recording element comprising a light-transmitting substrate and a photoconductive layer thereon, and said substrate facing said light pipe at said transfer station, and said means to reduce the electrostatic attraction between said toner particles and said recording element comprising light-emitting portions in said light pipe at said transfer station to direct light to said photoconductive layer through said light-transmitting substrate.
 8. Apparatus for transferring magnetic toner particles, adhered by electrostatic attraction in an image configuration on a recording element, to an image-receiving surface of a transfer member, said apparatus comprising: guide means to dispose said recording element adjacent said image-receiving surface of said transfer member with said toner particles facing said image-receiving surface at a transfer station, means to reduce the electrostatic attraction between said toner particles and said recording element, means to provide a magnetic field between said recording element and said transfer member to magnetically attract and thereby transfer said toner particles to said image-receiving surface, said magnetic toner particles comprising an electrically conductive core having a coating of a thermoplastic adhesive thereon, said recording element comprising a light-transmitting substrate and a photoconductive layer thereon, said guide means comprising a light pipe having a wall for guiding said recording member with its substrate facing said wall, said guide means also comprising a guide member having a wall for guiding said transfer member, heating means being cooperatively associated with said guide member to heat it and said transfer member, and said means to reduce the electrostatic attraction between said toner particles and said recording element comprising a light-emitting portion in said light pipe at said transfer station to direct light to said photoconductive layer through said light-transmitting substrate.
 9. Apparatus as defined in claim 8, wherein said wall of said light pipe and said wall of said guide member are arcuate in shape and curved in opposite directions, said walls being nearest to each other at said transfer station, and said light pipe and said guide member are adjustably disposed with respect to each other.
 10. In apparatus of the type wherein the photoconductive layer of a recording element comprising a photoconductive layer on a substrate, is electrostatically charged, exposed with a light image to provide an electrostatic latent image, and developed with magnetic toner particles adhered by electrostatic attraction to said latent image to provide a powder image, the improvement of means to transfer said powder image to a surface of a transfer member comprising: a transfer station, means to dispose said recording element with said powder image at said transfer station, means to dispose said transfer member with said surface adjacent to, but slightly spaced from, said powder image at said transfer station, means to provide a magnetic field at said transfer station, means to reduce the electrostatic attraction between said toner particles and said photoconductive layer at said transfer station and to cause said toner particles to be magnetically attracted to said surface of said transfer member, means to fix said transferred toner particles to said surface, said means to dispose said recording element with said powder image at said transfer station comprising a light pipe with a wall for guiding said recording element to said transfer station, and said means to reduce the electrostatic attraction between said toner particles and said photoconductive layer comprising light-emitting portions in said wall of said light pipe at said transfer station and a light source for providing light to said light-emitting portions at said transfer station, said substrate being light transmitting. 